Research On Exfoliation Behavior Of Oxides On Boiler Tubes By In-Situ SEM Observation

Super(super)critical unit boiler tube in the supercritical steam environment can react directly with the steam,easily oxidized to form an oxide film.When the oxide film reaches a certain thickness under the influence of internal and external stress,a certain degree of peeling occurs.Flaking of the oxide film will plug the boiler tube flow part of the boiler tube caused by short-term over-temperature burst tube,while the oxide film will fall into the steam turbine erosion turbine flow path and a series of issues.Therefore,it is necessary to analyze and study the mechanism of the growth and flaking of the oxide film in the boiler tubes of power plants,and provide a theory for the efficient and safe operation of super(super)critical boiler units stand by.In this paper,the growth and spalling behavior of P92 steel were studied,including supercritical water oxidation experiment and in-situ tensile experiment.We first performed a series of supercritical oxidation experiments on P92 steel in a supercritical reactor.After oxidation experiments,we recorded the oxidation weight gain of the samples and analyzed the growth kinetics of P92.The surface morphology of the samples was examined by microscopic examination.,Cross-section morphology and elemental distribution were analyzed and su mmarized,the mechanism of oxide film formation and growth was systematically revealed.The exfoliation of the oxide film is due to the difference of the strain of the substrate / oxide film,and the strain and strain accumulate in the oxide film,so we can use the in situ tensile experiment to simulate the oxidation of the boiler tube strain film.The results show that the initial stress value of the oxide film is close to the theoretical value.The failure mode of the oxide film under tensile stress is ma inly through the thickness of the crack,the nucleation of the crack in the oxide layer has holes or defects,The crack spacing becomes smaller as the tensile stress increases,and the crack spacing appears equally spaced,and the formation of crack penet rating through the thickness of the oxide film has an effect on the plane stress in the oxide film and the stress distribution of the oxide film substrate.